Best Driveshaft?
From your sig it appears that you are using the stock 10-bolt. If this is true, be aware that neither the Nitrous Ready shaft nor the HD Aluminum shaft are available with 1310 yoke.
I have a shudder that seems like the driveshaft is out of balance. It only occurs between 50 and 57 mph (and is more noticeable when decelerating). I took it to the dealer and they replaced the coupler near the rear end. It improved it a bit, but the shudder is still there. Should they be replace the forward coupler as well? Is there something else that could be loose that is causing this?

